Reviewed by: HU Medical Review Board | Last Reviewed: January 2016.

Crohn’s disease is an inflammatory disease of the digestive tract. For most people, inflammation is the only feature of Crohn’s disease at diagnosis.1 However, the disease tends to progress over time.2 By 5 years after diagnosis, about half of people with Crohn’s disease have complications. By 10 years, about 70% have complications.1

Factors that make complications more likely are:1

  • Crohn’s disease onset before age 40 years.
  • Having perianal disease when you are diagnosed.
  • Needing steroids during the first disease flare.

New treatments may slow disease progression and the frequency of complications.2

Crohn’s disease complications

In Crohn’s disease, the inflammation goes through the full thickness of the intestinal walls. (By comparison, the inflammation in ulcerative colitis only affects the innermost layer of the intestinal wall.) Some of the common Crohn’s disease complications happen because the inflammation is so deep.

Inflammation eventually causes scarring in your intestine. As the scar tissue builds up, it becomes harder for food and waste to pass through the digestive tract. A stricture is a narrow area of the digestive tract. Ulcers and lesions are other signs of damage to the lining of the intestine.

An abscess is a large inflamed mass.2 An abscess forms when the inflammation extends deep into wall of the intestine. The abscess is way of containing an infection and preventing its spread to the rest of the body. Abscesses are fairly common complications of Crohn’s disease. They affect 10% to 30% of patients.3

Overtime, an abscess can cause abnormal connections to form between the intestine and other organs.3 These connections are called fistulas. Fistulas can develop between different loops of the intestine. They also develop between the intestine and other structures, such as the bladder or skin. Fistulas can also cause an abscess to develop. Fistulas allow stool and other infectious material to travel to parts of the body where it does not belong. An abscess may form as a way of containing this material.

Crohn’s disease can be a cause of anal fissures. An anal fissure is a split or tear at the end of the anal canal. Anal fissures are often painful, but usually heal on their own.

Toxic megacolon is a rare but serious complication of inflammatory bowel disease.4 For unknown reasons, the colon begins to widen (dilate). Toxic megacolon causes symptoms such as bloody diarrhea, abdominal pain, fever, and rapid heart beat. If left untreated, it could lead to shock or a tear (perforation) in the colon.

Related digestive diseases

Crohn’s disease also can increase your risk of certain digestive tract diseases.

Between 13% and 34% of people with Crohn’s disease have gallstones.5 Gallstones are hard particles that form in the gallbladder.6 The gallbladder stores bile. Bile is a liquid that your liver makes to help you digest fat. Two components in bile are bile salts and bilirubin. Crohn’s disease changes the way bile salts and bilirubin are absorbed in the intestine.7 It also causes changes in diet and gut bacteria. These changes make gallstones more likely.

People with Crohn’s disease have a higher-than-average risk of colon cancer.8 This is particularly true for people with Crohn’s colitis or ileocolitis. Risk is highest for people who were diagnosed with Crohn’s disease at a young age and people with more Crohn’s complications.

Inflammatory bowel disease can overlap with several different liver diseases. Simply having inflammatory bowel disease is a risk factor for primary sclerosing cholangitis (PSC). PSC is a disease that causes inflammation and scar formation in the bile ducts.9Methotrexate, a medication that treats inflammatory bowel disease, can cause liver damage.10Corticosteroids cause weight gain, which increases the risk of fatty liver disease. Immunosuppressants may reactivate hepatitis viruses that can damage the liver.

Other related health problems

Although it is a digestive disease, Crohn’s disease affects the whole body. People with Crohn’s disease are at risk for malnutrition. There are many factors that contribute to malnutrition. These factors include difficulty consuming a varied and adequate diet, trouble absorbing nutrients, and medication side effects.

Anemia is the most common complication of inflammatory bowel disease outside the digestive tract.11 Anemia may result from malnutrition, blood loss, or malabsorption. It can also be an adverse effect of some medications.

Osteoporosis —weakened bones— affects about 12% to 16% of people with Crohn’s disease.12 The link between these conditions may be due to a combination of treatment with corticosteroids, inflammation, and difficulty consuming foods with calcium and vitamin D.

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